Timothy Peter Johnson (December 28, 1946 – October 8, 2024) was an American lawyer and politician who served as a United States senator from South Dakota from 1997 to 2015. A member of the Democratic Party, he served as the United States representative for South Dakota's at-large congressional district from 1987 to 1997 and in the state legislature from 1979 to 1987. Johnson is the last Democrat to hold statewide and/or congressional office in South Dakota. He and Stephanie Herseth are also the last Democrats to win a statewide election in South Dakota.

Johnson was born in Canton, South Dakota, the son of Ruth Jorinda (née Ljostveit), a homemaker, and Vandel Charles Johnson, an educator. He had Norwegian, Swedish, and Danish ancestry. Raised in Vermillion, Johnson earned a Bachelor of Arts in 1969 and a Master of Arts in 1970, both in political science, from the University of South Dakota, where he was a member of the Delta Tau Delta fraternity.

After doing post-graduate studies at Michigan State University from 1970 to 1971, a period during which he worked for the Michigan Senate, Johnson returned to Vermillion to attend the University of South Dakota School of Law and earned his Juris Doctor in 1975; he went into private practice immediately thereafter. He did not take the bar exam as he was admitted to the South Dakota bar under the state's diploma privilege.

Johnson served in the South Dakota House of Representatives from 1979 to 1982 and in the South Dakota Senate from 1983 to 1986. He served as Clay County deputy state's attorney in 1985 during his tenure in the South Dakota Senate. He was elected to the United States House of Representatives from South Dakota's at-large congressional district in 1986. During his first term, he introduced more legislation than any other freshman member of the House. Between 1991 and 1994, he served as a regional whip for the Democratic Party. He left the House in 1997, when his Senate tenure began.

Johnson's Senate career began in 1997.

In December 2006, Johnson suffered a brain hemorrhage. His condition was viewed with much suspense; Democrats held a one-seat Senate majority, and had Johnson died or resigned, Governor Mike Rounds would likely have appointed a Republican to Johnson's seat, giving Republicans control of the Senate. Johnson returned to his full Senate schedule on September 5, 2007, to both tributes and standing ovations.

Johnson chose not to seek reelection in 2014.

Johnson was considered a centrist Democrat.